Design Procedures for Hinge Restrainers and Hinge Seat Width for Multiple-frame Bridges
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The collapse of bridges in recent earthquakes due to hinge unseating emphasized the importance of providing an adequate number of hinge restrainers to limit the relative displacement between hinges. A nonlinear numerical model representing the longitudinal earthquake response of two frames connected at a hinge is thus developed. A parameter study shows that the response of the hinge is governed by the frame period ration, the target ductility demand of the frames, and the stiffness of the hinge restrainers. A multiple-step design procedure based on a linearized numerical model, is developed. The procedure accounts for the phasing between frames with a modal analysis. Yielding of frames is linearized by using a substitute structure method, and optimization theory is used to obtain the restrainer stiffness. A simplified single-step restrainer design procedure for binge restrainers is also developed. Comparisons with current restrainer design procedures show that the new multiple-step and single-step procedures are more accurate than current procedures for designing hinge restrainers. Pounding of frames and engaging of restrainers produce forces and displacements significantly different than what is typically assumed in design. Pounding typically increases the demand on stiffer frames and decreases the demand on most flexible frames. Although estimates from bounding models generally report the maximum elastic forces, they do not bound frame ductility.